Although not limited to such an application, the invention will be described more particularly with reference to a tire.
The reinforcement armature or reinforcement of tires is, at the present time—and usually—formed by a stack of one or more plies conventionally denoted by “carcass plies”, “crown plies”, etc. This way of denoting the reinforcements derives from the manufacturing process, which consists in producing a series of semifinished products in the form of plies, provided with filamentary reinforcing elements that are often longitudinal, which reinforcements are subsequently assembled or stacked so as to build up a tire blank. The plies are produced flat, with large dimensions, and are subsequently cut according to the dimensions of a given product. The plies are also assembled, firstly, substantially flat. The blank thus produced undergoes a forming operation so as to adopt the typical toroidal profile of tires. Semifinished products called “finishing products” are then applied to the blank, in order to obtain a product ready for vulcanization.
Such a “conventional” process involves, in particular as regards the phase of producing the tire blank, the use of an anchoring element (generally a bead wire), used for anchoring or retaining the carcass reinforcement in the region of the tire beads. Thus, for this type of process, a portion of all of the plies making up the carcass reinforcement (or only part of it) is upturned around a bead wire placed in the bead of the tire. In this way, the carcass reinforcement is anchored in the bead.
Generalization in the industry using this type of conventional process, despite many variants in the way in which the plies are produced and assembled, has led those skilled in the art to use a vocabulary derived from the process: hence the generally accepted terminology comprising in particular the terms “plies”, “carcass”, “bead wire”, “forming”, for denoting the passage from a flat profile to a toroidal profile, etc.
At the present time there are tires that do not comprise, strictly speaking, “plies” or “bead wires” according to the above definitions. For example, document EP 0 582 196 discloses tires produced without using semifinished products in the form of plies. For example, the reinforcing elements for the various reinforcement structures are applied directly to the adjacent layers of rubber compounds, the combination being applied by successive layers on a toroidal core, the shape of which makes it possible to obtain, directly, a profile matching the final profile of the tire being manufactured. Thus, in this case, there are no longer “semifinished products”, nor “plies” nor a “bead wire”. The base products, such as the rubber compounds and the reinforcing elements in the form of cords or filaments, are applied directly to the core. Since this core has a toroidal shape, there is no longer a forming operation for bringing the blank from a flat profile to a toroidal profile.
Moreover, the tires described in that document do not have a “conventional” upturn of the carcass ply around a bead wire. This type of anchoring is replaced with an arrangement in which circumferential cords are placed adjacent said sidewall reinforcement structure, the combination being embedded in an anchoring or bonding rubber compound.
There are also processes for assembly on a toroidal core using semifinished products suitable for rapid, effective and simple application on a central core. Finally, it is also possible to use a hybrid construction, comprising both certain semifinished products for achieving certain architectural aspects (such as plies, bead wires, etc.), whereas others are produced by directly applying reinforcing elements and/or compounds.
In the present document, so as to take into account recent technological developments both in the manufacturing field and in product design, the conventional terms such as “plies”, “bead wires”, etc. are advantageously replaced with neutral terms or terms that are independent of the type of process used. Thus, the term “carcass reinforcement” or “sidewall reinforcement” is valid for denoting the reinforcing elements of a carcass ply in the conventional process, and the corresponding reinforcing elements, generally applied in the sidewalls, of a tire produced using a process without semifinished products. For its part, the term “anchoring region” may denote both the “conventional” carcass ply upturn around a bead wire of a conventional process and the assembly formed by the circumferential reinforcing elements, the rubber compound and the adjacent sidewall reinforcement portions of a base region produced using a process with application on a toroidal core.
The longitudinal direction, or circumferential direction, of the tire is the direction corresponding to the periphery of the tire and is defined by the run direction of the tire.
A circumferential plane or circumferential sectional plane is a plane perpendicular to the rotation axis of the tire. The equatorial plane is the circumferential plane passing through the center or top of the tread.
The transverse or axial direction of the tire is parallel to the rotation axis of the tire.
A radial plane contains the rotation axis of the tire.
The performance of a tire, especially as regards grip, endurance, wear resistance and running comfort, is dependent on various components of the tire such as the choice of crown architecture and the choice and nature of the rubber compounds constituting the various parts of the tire. For example, the nature of the rubber compounds constituting the tread have an impact on the properties of said tire, such as the wear and grip properties.
Moreover, it is also known to those skilled in the art that the physico-chemical properties of rubber compounds vary with the use to which the tire is put and especially as a function of temperature, which for example has an influence on the properties of the tread of a tire. Thus, when a vehicle is being used, the rubber compounds forming the various parts of the tire, such as the base regions, the sidewalls and the tread, are subjected to stresses which result in the compounds rising in temperature and therefore in variations in the physico-chemical properties of said compounds. It is known, for example, that, depending on the type of tire and its use, certain regions of the tire are subjected to stresses such that the temperatures reached may result in non-optimal performance of the tire, in terms of grip or wear.
It is thus desirable to be able to measure a temperature or else another physical parameter of the tire and especially of the rubber compounds of which it is made, especially so as to help the driver or rider of the vehicle to adapt his operation to the conditions and thus optimize the performance of the tire.
It is known, for example from document EP 1 275 949, to implant a wireless sensor in tires so as to determine forces or stresses exerted within the tire.
Document EP 0 937 615 discloses the use of wireless surface acoustic wave sensors incorporated into a tire, especially for measuring the grip of a tire. Such a sensor has the advantage of being able to be remotely interrogated wirelessly, by radio waves, without a nearby energy source being necessary. The energy of the interrogating radio wave sent by a remote interrogation device is sufficient for the sensor to transmit a modified radio wave in response.
Wireless SAW (surface acoustic wave) or BAW (bulk acoustic wave) sensors may thus be used in tires to measure physical parameters. One important advantage is that they can be remotely interrogated by radio waves, without a nearby energy source being necessary.
However, in the case of SAW or BAW sensors of the resonator type, unlike SAW or BAW sensors of the delay line type, whenever at least two measurement devices of this type, using the same frequency band, are inserted into a tire, an associated interrogation device is not capable of identifying the source of the signals that it receives, and therefore of identifying the sensor with which it communicates. This is because the use of several SAW or BAW sensors of the resonator type does not allow signals to be transmitted by each of them that permit their identification when they work within the same frequency band.